Working directly with the crown through PCP is not recommended (and I don’t even know if it is possible).
The best option, in my opinion, is as follows:
1) Create a database and a table in which your tasks will be stored (if necessary, another table or file in which there will be an execution log).
2) Write a pkhp script that will check this table and execute scripts whose time has come, but it’s not worth checking.
3) Add a task in crown to run this script, for example, every hour (yes, at least every 10 minutes or a minute).
In this case, you will have every opportunity to complete the work and establish a schedule.
In theory, there is not enough point 4 here - to make an API for working with your system (adding / changing / deleting tasks, getting a list of tasks, etc.).
PS Here I found the material on working with the crown directly from the PCP. There are still various ways through which you can directly change the file / etc / crontab, but IMHO is a bad style to give access to the user php to work directly with cron.